The disclosure of Japanese Patent Application No. HEI 11-366592 filed on Dec. 24, 1999 including the specification, drawings, and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to an internal combustion engine mounted in a vehicle and the like. In particular, the invention relates to an internal combustion engine having a variable valve mechanism capable of arbitrarily altering the opening and closing timing and/or the opening amount of an intake valve and exhaust valve, and to a control method therefor.
2. Description of Related Art
Recent years have seen advances in the development of internal combustion engines for mounting in a vehicle and the like that are provided with a variable valve mechanism capable of arbitrarily altering the opening and closing timing and/or the opening amount of at least one of an intake valve and an exhaust valve with the aim of improving exhaust emissions and reducing fuel consumption.
An electromagnetic drive type moving valve mechanism has been proposed as an example of a variable valve mechanism for driving an intake valve and an exhaust valve of an internal combustion engine to open and close using electromagnetic force. In this electromagnetic drive valve type of moving valve mechanism, because there is no need to drive the intake and exhaust valve to open and close using the rotation force of the engine output shaft (crankshaft), loss in mechanical output originating in the drive of the intake and exhaust valve is prevented.
Moreover, because it is also possible to open and close the intake and exhaust valve at the desired timing with no limitations imposed by the position of rotation of the engine output shaft, it is possible to control the amount of air intake into each cylinder without using an intake aperture valve (a throttle valve). As a result, pumping loss in the air intake caused by the throttle valve can be suppressed and the amount of fuel consumption of the internal combustion engine can be reduced.
Moreover, in an internal combustion engine mounted in a vehicle and the like, fuel cut control, in which fuel injection is halted when the vehicle is running in a state of deceleration, is performed in order to reduce emissions and reduce the amount of fuel consumption.
Namely, when the fuel injection is halted while the engine output shaft of the internal combustion engine is in a state of rotation, generation and combustion of the air-fuel mixture in the internal combustion engine does not take place and air that has been taken into the internal combustion engine is expelled in its existing state. As a result, as well as the amount of fuel consumption in the internal combustion engine being improved, emissions are reduced.
Moreover, exhaust purifying catalysts are provided in the exhaust system of an internal combustion engine mounted in a vehicle and the like for purifying harmful gas components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust gas expelled from the internal combustion engine.
However, because these exhaust purifying catalysts have catalytic substances such as platinum (Pt), palladium (Pd), rhodium (Rh) and the like on the surface of a catalyst carrier in which a plurality of exhaust flow passages are formed, if the above described fuel cut control is performed and the concentration of oxygen in the exhaust gas increases, there is a tendency for oxygen and various oxides to adhere to the surface of the catalytic substance. This phenomenon is most marked when the temperature of the exhaust purifying catalyst is high and, in some cases, has caused the purifying capability of the catalytic substance to deteriorate.
In response to this, it is possible to consider a method in which fuel cut control is prohibited when the temperature of the exhaust purifying catalyst rises above a predetermined temperature, however, the problem then is that this leads to increases in the amount of fuel consumption and emissions.
To counter such problems, a valve timing control device for an internal combustion engine has been proposed in Japanese Patent Application Laid-Open (JP-A) No. 10-115234.
The valve timing control device for an internal combustion engine described in the above publication operates in the following manner. An internal combustion engine is provided with a camshaft for driving an intake valve and an exhaust valve to open and close using the rotation force of the engine output shaft and also provided with a variable valve mechanism for altering the opening and closing timing of the lift amount of the intake valve and/or the exhaust valve. When fuel cut control is performed, the variable valve mechanism is controlled so as to shorten the time that the intake valve is open in the air intake step of each cylinder, thereby reducing the amount of air flowing from the intake system to the exhaust system and, accordingly, suppressing deterioration of the exhaust purifying catalyst caused by oxygen.
Because there is only a small amount of air flowing from the intake system of the internal combustion engine to the exhaust system thereof, it is possible to delay the advance of the deterioration of the exhaust purifying catalyst caused by oxygen. However, it is difficult to completely prevent deterioration of the exhaust purifying catalyst caused by oxygen.
In particular, because the exhaust purifying catalyst is easily deteriorated due to oxygen when the temperature of the exhaust purifying catalyst is high, the concern exists that the exhaust purifying catalyst will deteriorate due to oxygen even when there is only a small amount of air flowing through the exhaust purifying catalyst.
An aim of the invention, therefore, is to provide a technology for preventing deterioration in the exhaust purifying catalyst due to fuel cut control and thereby improving the durability of the exhaust purifying catalyst in an internal combustion engine.
A first aspect of the invention is an internal combustion engine having a variable valve mechanism capable of altering opening and closing timings and/or opening amounts of at least one of an intake valve and an exhaust valve of an internal combustion engine; a fuel injection valve for supplying fuel either directly or indirectly to a combustion chamber of the internal combustion engine; and a forcible valve closing device that controls at least one of the intake valve and the exhaust valve to be closed when the fuel injection valve is prohibited from operating.
In an internal combustion engine having a variable valve mechanism structured in this way, when the fuel injection valve is prohibited from operating, the forcible valve closing device controls the variable valve mechanism such that at least one of the intake valve and exhaust valve to be in a closed state.
When at least one of the intake valve and exhaust valve is placed in a closed state in an internal combustion engine, there is no flow of air from the intake system to the exhaust system of the internal combustion engine. As a result, the exhaust system of the internal combustion engine is not placed in an oxygen abundant atmosphere, and the exhaust purifying catalyst provided in the exhaust system is not placed in an oxygen abundant atmosphere.
Moreover, in the internal combustion engine having a variable valve mechanism according to the invention, the forcible valve closing device may also synchronize for each cylinder a timing when the fuel injection valve is prohibited from operating with a timing when the intake valve and/or the exhaust valve are placed in a closed state.
This is to prevent events such as the following from occurring:
(1) If the timing at which the intake valve is placed in a closed state is earlier than the timing at which the fuel injection valve is prohibited from operating, then in an intake port injection type of fuel combustion engine, fuel injected from the fuel injection valve adheres to the intake port and intake valve and, when the fuel cut control is ended, the adhered fuel is taken into the cylinders together with the fuel newly injected from the fuel injection valve, thereby placing the interior of the cylinders in a fuel abundant atmosphere.
(2) If the timing at which the intake valve is placed in a closed state is later than the timing at which the fuel injection valve is prohibited from operating, then air flows from the intake system of the internal combustion engine to the exhaust system thereof, and the exhaust purifying catalyst provided in the exhaust system is placed in an oxygen abundant atmosphere.
(3) If the timing at which the exhaust valve is placed in a closed state is earlier than the timing at which the fuel injection valve is prohibited from operating, there is back flow into the intake system of non-combusted fuel-air mixture and combusted gas in the combustion chamber.
(4) If the timing at which the exhaust valve is placed in a closed state is later than the timing at which the fuel injection valve is prohibited from operating, then air flows from the intake system of the internal combustion engine to the exhaust system thereof, and the exhaust purifying catalyst provided in the exhaust system is placed in an oxygen abundant atmosphere.
In an internal combustion engine having a variable valve mechanism according to the invention, the variable valve mechanism is controlled such that at least one of the intake valve and the exhaust valve is placed in a closed state only when the injection of fuel from the fuel injection valve is prohibited and the temperature of the exhaust purifying catalyst provided in the exhaust system of the internal combustion engine is equal to or greater than a predetermined temperature.
A second aspect of the invention is an internal combustion engine having a variable valve mechanism capable of altering opening and closing timings and/or opening amounts of at least one of an intake valve and an exhaust valve of an internal combustion engine; a fuel injection valve for supplying fuel either directly or indirectly to each cylinder of the internal combustion engine; and valve timing altering device that alters the timings at which the intake valve and exhaust valve are opened and closed are set at the timings at which gas flows from the exhaust system to the intake system of the internal combustion engine when the fuel injection valve is prohibited from operating.
In an internal combustion engine having a variable valve mechanism structured in this way, when the fuel injection valve is prohibited from operating, the valve timing altering device controls the variable valve mechanism such that the timing at which the intake and exhaust valves are opened and closed is set at the timing at which gas flows from the exhaust system to the intake system of the internal combustion engine.
In this case, gas flows from the exhaust system to the intake system of the internal combustion engine, and there is no flow of air from the intake system to the exhaust system of the internal combustion engine. As a result, the exhaust system of the internal combustion engine is not placed in an oxygen abundant atmosphere, and the exhaust purifying catalyst provided in the exhaust system is not placed in an oxygen abundant atmosphere.
At the same time as the timings of the opening and closing of the intake and exhaust valves are set as the timings at which gas flows from the intake system to the exhaust system of the internal combustion engine in a portion of the cylinders of the internal combustion engine, in the remaining cylinders, the timings of the opening and closing of the intake and exhaust valves are set as the timings at which gas flows from the exhaust system to the intake system of the internal combustion engine.
In this case, because the gas flowing from the intake system to the exhaust system via a portion of the cylinders is drawn back to the intake system from the exhaust system via the remaining cylinders, no air passes through the exhaust purifying catalyst.
Moreover, in the internal combustion engine having the above described variable valve mechanism, it is also possible for the valve timing altering means to synchronize for each cylinder a time when the fuel injection valve is prohibited from operating with a time at which the timings of the opening and closing of the intake valve and the exhaust valve are altered.
Moreover, in the internal combustion engine having the above described variable valve mechanism, it is also possible for the variable valve mechanism to alter the timings at which the intake valve and the exhaust valve are opened and closed only when the injection of fuel from the fuel injection valve is prohibited and the temperature of the exhaust purifying catalyst is equal to or greater than a predetermined temperature.
Any of the following exemplary variable valve mechanisms may be used according to the invention: an electromagnetic drive type moving valve mechanism in which the intake and exhaust valves are driven using electromagnetic force; a hydraulic drive type moving valve mechanism moving valve mechanism in which the intake and exhaust valves are driven using hydraulic force; a variable valve mechanism in an internal combustion engine provided with a camshaft that drives the intake and exhaust valves, wherein the variable valve mechanism switches between operating and stopping the intake and exhaust valves by switching the mode of transmission of the driving force between the camshaft and the intake and exhaust valves; or a variable valve mechanism in an internal combustion engine provided with a camshaft that drives the intake and exhaust valves, wherein the variable valve mechanism alters the opening and closing timings of the intake and exhaust valves by altering the rotation phase of the camshaft relative to the crankshaft.